In analog integrated circuits, when a reference voltage not dependent on the temperature and power source voltage was used, a reference voltage circuit called a “bandgap circuit” was used. Mounting together with digital circuits is easy, so even in important CMOS analog integrated circuits, bandgap circuits are being widely used as stable reference voltage circuits.
In a related bandgap circuit, the potential of a forward-biased pn junction and a voltage proportional to the absolute temperature (T) (in general, called PTAT) are added to obtain a reference voltage not dependent on the temperature. Various types of such circuits have been provided.
It is known that the potential of the forward-biased pn junction (if approximating the potential of the pn junction by a linear equation or within the range able to be approximated by a linear equation) is the CTAT (complementary-to-absolute temperature). Further, it is known that by adding a (suitable) PTAT voltage to the potential of this forward-biased pn junction, a reference voltage substantially not dependent on temperature is obtained.
Incidentally, in the past, various techniques have been proposed for adjusting the value of the VBGR.    Patent Document 1: Japanese Laid-open Patent Publication No. H08-018353    Patent Document 2: Japanese Laid-open Patent Publication No. 2005-182113    Patent Document 3: U.S. Pat. No. 5,325,045